The present invention relates to aircraft electric start motors, and more specifically, to motor controllers for managing thermal stress associated with electrical start of aircraft engines.
The engines in an aircraft are typically started by non-electrical methods, for example, a start turbine driven by compressed air. An increased number of aircrafts in recent years have begun to use electric generators to start the engine by operating the generator in motoring mode, powered by a motor controller. The motor controllers on aircraft are typically designed for other continuous duty applications, such as, cabin air compressor, air recirculation fans, and fuel pumps. When there is a need for an engine start, typically one or two of the available motor controllers are called upon from their normal duty to start the engine, and then returned to their normal duty. Because of the very high thermal stress to the motor controller semiconductor power switches (e.g., an insulated gate bipolar transistor (IGBT) switch) during an engine start, however brief this engine start duty may be, the IGBT switch in conventional motor controllers are sized for this brief engine start duty, or an additional motor controller is used in parallel. As a result, the motor controller becomes heavier, or if parallel motor controllers are used, the system weight increases due to additional power feeders and contactors.